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Now we just need Qt5.2, Mesa 9.2 (forgot why), and well, I don't know if KWin will keep using the Qpainter compositor, that Martin made, but if so, and if KDE 4.12 is based on Qt5.2, then at least KWin in KDE 4.12 is pretty far by Jan/Feb next year, if I've understood everything correctly

No, you didn't.

1.) There is no KDE 4.
2.) No 4.x release of Software Compilation will be based on Qt 5.
3.) SC 4.11 is the last release featuring Plasma Workspaces components, including KWin.
4.) The Workspaces parts of SC 4.11 will be supported for 2 years, maybe longer.
5.) Plasma Workspaces 2 will feature KWin 5.0.
6.) KWin 5.0 will be the first KWin release fully supporting Wayland.
7.) PW2 will be released sometime in 2014 but probably not as early as January or February.
8.) Read Planet KDE to get correct news and you won't misunderstand it all any longer.

The primary supported method to write apps for Ubuntu, Tizen and FirefoxOS is HTML5. I think Sailfish will be able to run apps for a wide range of platforms (Qt/native, MeeGo, Android and HTML5).

Actually QML and HTML5 are the official development platforms for Ubuntu Mobile, as with Jolla.
FirefoxOS is HTML5 only, however since the Mozilla Marketplace is cross platform it will probably have more success than other HTML5 platforms such as Tizen.
Tizen also suffers from an unclear development path and lack of official support for any native applications as EFL is no longer a supported framework.